Anode protection technology in sulfuric acid equipment

The website of Nanjing Gaoyuan Environmental Protection Engineering Co., Ltd. has a detailed introduction.

] Lanzhou Xingye’s technology in this area is relatively mature. You can check it online.

Anode protection technology is a very mature technology and can be found online.

1. Anti-corrosion principle of anode protection: Anodic protection is one of the electrochemical anti-corrosion technologies, which is based on the anodic passivation of metals. There are currently two blunt mechanisms: (1) Oxide film theory: It is believed that the surface of passivated metal is covered by an oxide film. The film has high stability and is not easily dissolved, thereby protecting the metal ； (2) Adsorption theory: It is believed that when the metal is passivated, a layer of oxygen atoms (or other atoms) is adsorbed on the surface, and the active valence of the atoms on the metal surface is saturated, or it is ionized by electrons in the metal to form an electric double layer structure, thus blocking the dissolution process of the metal anode and making the corrosion rate extremely low. The anti-corrosion mechanism of anode protection cooler can be summarized as: When the protected metal equipment is supplied with anode current, a high-resistance passivation film is formed on the metal surface, thus preventing further corrosion of the metal. The essence of using anode protection is to pass a certain amount of current to the stainless steel so that the potential of each part is maintained in the passivation zone. If the current is too large, over-passivation corrosion will occur; if the current is too small, the passivation film cannot be maintained and activation will occur. After activation, the passed anode current will accelerate the corrosion of stainless steel, which is called electrolytic corrosion. It is difficult to passivate carbon steel in hot concentrated acid, and the corrosion rate after passivation is also relatively large, and the stability of the passivation film is relatively poor. Therefore, anode protection coolers are almost entirely made of stainless steel. 2. Anode protection structure and materials: The shell-and-tube anode protector looks like a tubular heat exchanger and is equipped with a power control system. The shell-and-tube anode protector is installed horizontally. It must maintain an inclination of 1 degree from the horizontal during installation, especially for coolers used for high-temperature absorption to prevent vaporization and vapor lock. In order to control the flow rate of acid and water and protect the normal operation of the anode, the inlet and outlet of the acid water are set above the cooler. The acid goes through the shell and the water goes through the tube. Tube and shell anode protector material: The tube shell is made of 304 stainless steel, the tube sheet and baffles are made of 316 stainless steel, the pipes are made of 316 stainless steel, and the pipe flange supports are made of 304 stainless steel. 3. Debugging before driving: 1. Pressure test: Before on-site installation, the acid side must undergo an air pressure or water pressure test. The test pressure is 0.4~0.45MPa. If the pressure does not decrease for half an hour and the weld does not leak, it is qualified. 2. Dry: After the pressure test, the acid side needs to be dried. Steam with a gauge pressure of 0.2~0.3MPa is used to dry the acid side through the water side in the tube. It is kept warm for about 24 hours. When the resistance between the anode and cathode is greater than 400 kiloohms, it is qualified. 4. Driving: 1. Turn on the cooling water: First open the water inlet and outlet valves of the cooler, and then start the cooling pump. Adjust the cooling water volume to reach the design value, the pressure is greater than 245 KPa, and regularly analyze the PH value and chloride ion content of the inlet and outlet cooling water. 2. Open acid cycle: Open the inlet and outlet valves first, and then start the acid pump. The acid side pressure drop is controlled at: Cooler to pump outlet: Less than 98KPa, from cooler to tower outlet: Less than 44.1KPa. 3. Enable the potentiometer (the following is for reference only, please refer to the actual instructions): for 93 acid: Control potential given value: -200mV, low control potential alarm value: -50mV, control potential high alarm value: -350mV ； A monitor high alarm value: -550mV, B monitoring high alarm value: -550mV, C monitoring high alarm value: ~mV. for 98 acid: Control potential given value: -300mV, control potential low alarm value: -150mV, control potential alarm value: -450mV ； A monitor high alarm value: -650mV, B monitoring high alarm value: -650mV, C monitoring high alarm value: ~ mV. 5. Operation of control system: Set the measurement selection switch to given, the working status switch to blunt, the power switch to ready, the monitoring parameter measurement to monitor 1, adjust the control potentiometer so that the potential displayed on the control display is slightly lower than the monitoring parameter display (for example, the monitoring parameter display is 50mV, then the control display should be adjusted to 60~80mV), then the power switch is set to work, and there will be current output after 30 seconds. At this time, when the measurement selection is set to protection, the protection value on the control display is consistent with the given value, which means constant potential. * * Works normally. Then slowly adjust the control potentiometer, do not let the current surge to 15A, and gradually move the protection potential to -200mV (drying acid) and -300mV (absorbing acid) respectively. The length of this process is related to the surface passivation state, acid concentration, and acid temperature. It can range from a few minutes to a few days. If the potentiostat cannot automatically maintain the potential, the current will often be cut off and the alarm will occur repeatedly. At this time, manual operation is required. Set the working switch to manual, the measurement selection switch to protection, and slowly adjust the manual potentiometer so that the displayed protection potential is -200mV (dry acid) or -300mV (absorbed acid). With the improvement of the passivation film, the protection potential will shift negatively, and the given current will be reduced. On the contrary, if the protection potential shifts forward, the current needs to be increased to bring it back to the normal value. Because it is manually adjusted, it is normal for the potential fluctuation to be within the range of 100mV. But it needs to be adjusted by a dedicated person.

http://bbs.hcbbs.com/viewthread.php?tid=106596&highlight=%D1%F4%BC%AB%B1%A3%BB%A4 Anode protection acid cooler, acid distributor, pipeline knowledge

Wuxi Neutral’s anode protection works well